[…] Me--who? (20)
If you had to sum up the whole theme of identity in two words, these two would likely do the trick. Throughout the whole poem the speaker is trying to answer the question he puts forth in these lines: "Who am I?" Except he's got a slangy conversational rhythm going on, so "me—who?" comes along and shortens the question up even more. In this form, we're able to see the frustration and confusion, the frantic feeling that can sometimes come along with searching for an answer to this question.
Well, I like to eat, sleep, drink, and be in love. (21)
That's a pretty simple way to sum up most people. This line comes at the beginning of a few more that name specific things the speaker likes, but the point here is that, as unique and different as people are from each other, at the end of the day our identities give us a lot in common.
You are white-- yet a part of me, as I am a part of you. That's American. (33)
Here, the "you" could be the speaker's instructor, or anyone who's reading this poem, even. Throughout the poem, the speaker has been debating how being black makes him different, or not, from white people. Here, he's starting to come to terms with the relationship between the two races. They may have their differences, but they're a part of each other, in America. It's interesting to think back to 1950, when this poem was written, and then think forward to today, and look at how the relationship between the two races has changed, and how it hasn't.